1. Field of the Invention
The present invention relates to a coating agent for drug releasing stents, a method for preparing the same and a drug releasing stent coated therewith. More particularly, the present invention relates to a coating agent for use in stents capable of controlled drug release, a preparation method thereof, and a drug releasing stent coated therewith.
2. Description of the Related Art
A stent is a tubular prosthesis or support, which is now widely used to hold open a natural conduit, such as a lumen, vessel, etc., to allow access for surgery or related invasive chemical treatment and to prevent the stenosis of the conduit. Furthermore, the insertion and expansion of a stent within the esophagus, the respiratory organs, the vessels, the urinary organs, and other lumens which are difficult to access has proven an influential therapy for diseases occurring therein.
A colo-rectal stent, developed in the late 1990's, can be used instead of an artificial anus for a patient who has undergone a surgical operation for rectal cancer. However, colorectal stents are not applicable to all patients who have undergone surgical operations for rectal cancer. Stent implantation is not a therapy for cancer, but a temporary treatment for preventing or counteracting disease-induced localized flow constriction, e.g., the narrowing of the intestine due to cancer. Typically, a colo-rectal stent is a tube made from metal wires, which is designed for insertion into a narrowed region of the large intestine and expansion thereat to counteract the flow constriction. For example, stents applicable to patients with colorectal cancer are commercially available in various types, and are most often made of a nickel and titanium alloy (commonly referred to as “Nitinol”).
Recently, many attempts have been made to improve therapeutic effects with stents, i.e., stent implants capable of delivering drugs, such as thrombolytic agents or antihyperplasia agents. For example, U.S. Pat. No. 5,092,877 discloses self-expanding stents to which drug release coatings are applicable. Also, PCT Publication No. WO 1996/032907 describes a drug release coated stent.
In order to release a biologically active material over a long period, a method for coating a stent with a drug has been studied. Typically, the biologically active material is dissolved in a polymeric solvent and the solution is applied to a stent, followed by removing the solvent to afford a biologically active material-coated stent.
When a biologically active material, such as dexamethasone, is selected for use in application to stents, attention must be paid to miscibility and compatibility with the solvent or polymers used and to the release rate.
Korean Patent No. 10-439156 discloses a coating composition for drug release stents and a preparation method thereof, in which a coating composition comprising 0.01-30 wt % of a co-precipitation of a biologically active material selected from dexamethasone, paclitaxel and mitomycin with a water-soluble polymer and 70-99.99 wt % of a crosslinking polymer solvent is applied to a stent.
Korean Patent. No. 10-511618 discloses a multi-layer coating for drug release-controllable stents and a method for the preparation thereof. The multi-layer structure is composed of a base layer made of poly(ethylene-co-vinylacetate) or styrenic rubber polymer, a second coating layer made of a biocompatible polymer and a drug, and a third coating layer made of a different drug. Examples of the biocompatible polymer include polyvinylalcohol, polyethylene glycol, polylactide, polyglycolide, polylactide copolymer, polyethylene oxide, polydioxanone, polycaprolactone, polyphosphagen, polyanhydride, polyaminoacid, cellulose acetate butylate, cellulose triacetate, polyacrylate, polyacrylamide, polyurethane, polysiloxane, polyvinylpyrrolidone, and copolymers thereof. The drug used in the second layer may be selected from among anti-platelet agent containing cilostazol (6-[4-(1-cyclohexyl-1Htetrazol-5-yl)butoxy]-3,4-dihydro-2(1H)-quinolinone, empirical formula C20H27N5O2, Mw 369.47), an anti-thrombolytic agent, an antihyperplasia agent, a growth factor, an antioxidant and a radio-active agent.